The present invention relates to air conditioning systems for automobiles and more particularly to a temperature control apparatus for an automobile air-conditioning system of a so-called reheat type in which the temperature of supply air is controlled by adjusting through an air mixing door the amount of the cooled air from an evaporator which is passed and heated through a heater core and the amount of the cooled air which bypasses the heater core.
In a known apparatus of this type, the temperature of supply air and hence the temperature inside the vehicle compartment of an automobile is controlled by adding together a value proportional to a temperature difference signal corresponding to the deviation or difference between a temperature preset by a temperature setting mechanism and the actual vehicle compartment temperature and a value derived by integrating the temperature difference signal to generate a temperature control signal and then controlling the position of the air mixing door within a range between a maximum heating position for supplying all the cooled air to the heater core and a maximum cooling position for supplying all the cooled air to bypass the heater core in accordance with the temperature control signal.
Also, it is so arranged that the amount of air flow from the blower is maintained at a minimum value as long as the temperature difference signal remains within a given range of positive and negative values, respectively, and upon exceeding the given range the amount of air flow is varied up to a maximum value in accordance with the value of the temperature difference signal.
As a result, the temperature control apparatus operates so as to satisfy the cooling power and the amount of heat required by the vehicle compartment by means of both the mixing ratio of heated or cooled air by the air mixing door and the amount of air flow from the blower.
In the air conditioning system, however, the cooling capacity of the evaporator is large as compared with the heating capacity of the heater core. Thus, the control characteristic of the temperature control apparatus must be varied depending on whether the heating or cooling is demanded.